Activation of the cyclic AMP pathway promotes serotonin-induced Ca2+ oscillations in salivary glands of the blowfly Calliphora vicina

Ca2+ and cAMP signalling pathways interact in a complex manner at multiple sites. This crosstalk fine-tunes the spatiotemporal patterns of Ca2+ and cAMP signals. In salivary glands of the blowfly Calliphora vicina fluid secretion is stimulated by serotonin (5-hydroxytryptamine, 5-HT) via activation of two different 5-HT receptors coupled to the InsP3/Ca2+ (Cv5-HT2α) or the cAMP pathway (Cv5-HT7), respectively. We have shown recently in permeabilized gland cells that cAMP sensitizes InsP3-induced Ca2+ release to InsP3. Here we study the effects of the cAMP signalling pathway on 5-HT-induced oscillations in transepithelial potential (TEP) and in intracellular [Ca2+]. We show: (1) Blocking the activation of the cAMP pathway by cinanserin suppresses the generation of TEP and Ca2+ oscillations, (2) application of 8-CPT-cAMP in the presence of cinanserin restores 5-HT-induced TEP and Ca2+ oscillations, (3) 8-CPT-cAMP sensitizes the InsP3/Ca2+ signalling pathway to 5-HT and the Cv5-HT2α receptor agonist 5-MeOT, (4) 8-CPT-cAMP induces Ca2+ oscillations in cells loaded with subthreshold concentrations of InsP3, (5) inhibition of protein kinase A by H-89 abolishes 5-HT-induced TEP and Ca2+ spiking and mimics the effect of cinanserin. These results suggest that activation of the cyclic AMP pathway promotes the generation of 5-HT-induced Ca2+ oscillations in blowfly salivary glands.